OPTIMIZATION OF OVERBURDEN BLASTING GEOMETRY BASED ON THE EFFECT OF BLASTHOLE DEPTH ON POWDER FACTOR AND EXPLOSIVES COSTS TO MEET PRODUCTION TARGET

Abstract

Blasting in overburden stripping strongly influences whether production targets are met and is also one of the largest operating cost items. This study examines how strongly blasthole depth affects powder factor (PF) and explosive cost, and then formulates an improved blast geometry so that the target of 200,000 BCM per cycle can be achieved more cost-efficiently. A quantitative approach with descriptive and comparative analysis was applied to one overburden blasting cycle at a coal mine in South Kalimantan, consisting of 334 blastholes 6.0–9.0 m deep drilled on an actual 7 m burden and 8 m spacing. Simple linear regression shows that hole depth is very strongly related to explosive charge (R² = 0.989), PF (R² = 0.957), and specific blasting cost (R² = 0.951). The actual geometry broke only 75.31% of the target at a PF of 0.341 kg/BCM. Three alternative geometries were designed using ICI Explosives criteria, all of which meet the target. The 8 m burden and 10 m spacing alternative performed best, giving a PF of 0.237 kg/BCM and a specific cost of Rp. 4,589.82/BCM, about 30% lower than the actual condition while requiring fewer holes. The findings indicate that increasing blasted volume is more effectively achieved by enlarging burden and spacing than by deepening the holes.